The motivation of frame rate up-conversion is that a video sequence with higher frame rate is generally considered to give higher quality experience than a video sequence with lower frame rate. The frame rate of a video sequence can be increased by inserting predicted frames in between existing frames. A good approach is to predict the in-between frame using bidirectional block based motion estimation, searching for linear motions between the previous frame and the next frame in the input video sequence. It is possible to use non-linear approaches that can represent acceleration, but the linear approach is used because of its simplicity and low complexity. The in-between frame is divided into blocks and to each of these a motion vector must be assigned in some way.
A problem or short-coming with many frame rate up-conversion algorithms is the handling of panning, rotating or zooming images. In FIG. 1, the camera pans to the left when going from image 20 to image 10, thus a new area becomes revealed along the left border of the image 10. There are parts of the audience and almost a whole commercial sign in the bottom image 10 that are not part of the top image 20. These “new” areas generally do not have any accurate references to the previous image 20. In clear contrast, pixel blocks in the new areas are typically encoded according to intra mode, or if being inter encoded, having motion vectors pointing to areas in the previous image 20 that look similar but will not represent the actual motion (the camera pan). The lack of accurate motion vectors for these pixel blocks makes rate up-conversion harder, possibly leading to visual artefacts in interpolated images.
Document [1] discusses the identification of a block Bi as an uncovered region, when it can be seen in a frame Ft to be determined and in a following frame Ft+1 but not in a previous frame Ft−1. Such a block is encoded as an intra block and has not been motion compensated by other blocks.